Freshman Rep. Scott Peters has earned the backing of the U.S. Chamber of Commerce, making the Californian one of the few House Democrats to earn the conservative-leaning group's endorsement this cycle and marking a huge development in what's expected to be one of the most competitive and costly House contests of the midterms.

Peters is facing Republican Carl DeMaio, a former San Diego City Council member who bills himself as a more moderate Republican, and who has earned praise from the GOP for being one of the party's best House recruits of 2014.

“We believe that your re-election to the U.S. House of Representatives will help produce sustained economic growth, help create jobs, and get our country back on track,” Chamber of Commerce President Thomas Donohue said in a letter to Peters, according to a Wednesday report from UT San Diego . “We will encourage the business community to vigorously support your candidacy.”

Last cycle, the chamber endorsed Peters' GOP opponent, former Rep. Brian Bilbray. Peters is being targeted by other GOP outside groups. Americans for Prosperity, the issue advocacy group tied to the Koch brothers, and Crossroads GPS, former White House aide Karl Rove's issue advocacy group, have already gone on air attacking Peters.

The chamber has yet to reserve ad time in the district, but the group spends millions each cycle on the candidates they endorse across the country. That means ads could come as Election Day nears.